Deletion mutations that fuse genes of the recombination-insertion section of bacteriophage lambda onto the bacterial promoter for tryptophan biosynthesis will be analyzed to ascertain the number and location of transcriptional stop signals, and the minimal genetic requirements for insertion and excision. The location of the promoter for constitutive integrase synthesis will be determined more precisely by genetic mapping of these deletions. Leftward transcription in the biotin gene cluster of Escherichia coli will be measured in strains where rightward transcription is eliminated by polar mutations or deletions. Holoenzyme synthetase will be assayed in mutants derepressed for biotin biosynthesis. Biotin sulfoxide reductase from Escherichia coli will be purified and characterized.